The present invention relates to digital video switchers, and more particularly to depth signal processing in a video switcher that includes depth based combining of video signals as well as processed depth outputs.
In the D1 4:2:2 digital video format three components of video data are transmitted or received: a luminance component (Y) for each pixel and two chrominance components (B-Y, R-Y) associated with each luminance component for alternate pixels, or picture elements. Therefore the sequence is: B1-Y1, Y1, R1-Y1; Y2; B3-Y3, Y3, R3-Y3; Y4; etc. Since each pixel has a luminance component, the luminance component is full bandwidth. However, only every other pixel has the chrominance components, so the chrominance components are one-half bandwidth. In this format a key source signal commonly is represented by using the Y-channel of the digital video stream. The Kaleidoscope digital video effects (video manipulation) product, the Kadenza digital switcher product and the Graphics Factory graphics generator product, all manufactured by The Grass Valley Group, Inc. of Grass Valley, Calif., United States of America, provide for depth information in the chrominance channels of the D1 channel containing the key source signal. The depth information ranges from full background (00000h) through normal screen depth (20000h) to full foreground (FFFFFh). Since the depth information is contained in the chrominance portion, it is in half-bandwidth form, i.e., two samples are needed for a complete depth sample and depth samples are provided for alternate pixels.
In a conventional small digital switcher there are generally one or more background signals, two video signals with associated key signals and a foreground signal as inputs. The two key video signals, KEY1 and KEY2, have a fixed priority with respect to each other so that one or the other of the video signals is always in front of the other as determined by such priority. The switcher combines the various input signals as layers, with the background layer underneath the other layers and the foreground layer over the other layers. The video layers lie between the foreground and background layers, with their relationship to each other, i.e., which layer is on top of the other, determined by the priority. The combining of these video layers is referred to as compositing. However once the layers have been combined, it is not possible to insert a new layer between the existing layers in a subsequent pass through the switcher. The new layers may only be placed in front of or behind the existing combined layers.
What is desired is processing of the video layers using depth information to provide dynamic key priority so that video layers may intersect or be placed at any depth with respect to prior composited video layers.